Recently, much attention has been paid to new and renewable energy or clean energy due to the problems of contamination of the environment and exhaustion of fossil fuels. Among them, energy using light is being spotlighted as a representative clean energy source capable of resolving the problems of contamination of the environment and exhaustion of fossil fuels. As representative energy using light, for example, there are photovoltaic cells such as solar cells, etc.
The photovoltaic cells are devices converting sunlight to electric energy, which are generally required to be exposed to external circumstances for a long time so as to easily absorb sunlight, and thus various types of packages are used to protect an internal device and the photovoltaic cells are manufactured in a unit form, which is typically referred to as a “PV module”.
Usually, the PV module includes a back sheet to protect the internal device (for example, a solar cell). FIG. 1 is a view illustrating a cross section of a solar cell module as a conventional PV module.
Referring to FIG. 1, the solar cell module usually has a structure in which transparent tempered glass 3 to which light is incident, a front encapsulant layer 2a, a plurality of solar cells C, a back encapsulant layer 2b, and a back sheet 1 are sequentially stacked. Further, the plurality of solar cells C are electrically connected to each other, and packed and fixed by the front and back encapsulant layers 2a and 2b. 
As an encapsulant forming the front and back encapsulant layers 2a and 2b, an ethylene vinyl acetate (EVA) copolymer is usually used. Since the ethylene vinyl acetate copolymer is advantageous in formability, a manufacturing cost, and physical properties such as transparency or the like, it has been widely used in the past.
However, the ethylene vinyl acetate copolymer has low moisture barrier properties, and thus resulting in low adhesive strength with the solar cell C or the transparent tempered glass 3 under conditions of a high temperature and high humidity, and the generation of delamination between the layers upon the long term use. Further, the ethylene vinyl acetate copolymer causes the corrosion of electrodes by generating a hydrolysis reaction due to the penetration of moisture, and also brings about the problems of air bubbles, etc. These problems eventually decrease efficiency when the encapsulants are applied to the solar cell module.
To address these problems, techniques using an ethylene/α(alpha)-olefin-based copolymer for the encapsulant are being attempted. Techniques related thereto are disclosed in Patent documents 1 and 2. The ethylene/α-olefin-based copolymer has moisture permeability lower than the ethylene vinyl acetate copolymer, does not generate hydrolysis reaction products such as acetic acid or the like, and thus can increase reliability of the solar cell module.
However, an encapsulant formed of the material of the ethylene/α(alpha)-olefin-based copolymer has low adhesion or the like, the problem of delamination attributable to low heat resistance due to a low melting point (Tm) in the solar cell module upon the long term use is still present, accordingly, the decrease in power output from the solar cell module is generated upon being applied to the PV module, and thus a solution is required.